Father Brown and Inspector Mallory are missing the morning after a visit to eerie Spencer Hall, and Edmund Noon is found dead in St Mary's churchyard next to grave of George and Jasmin Haggard, whom he is believed to have murdered. Noon had lured both Mallory and Brown to profess his innocence of the crime. Without their leaders, sergeant Goodfellow, Mrs McCarthy and Bunty must reason and deduction, seeking clues themselves, to find the missing men, who are chained up underground, with oxygen running out. Beggar veteran Harold "Blind 'Arry" Slow earns McCarthy's gratitude, having refused payment standing watch and finding a crucial key in the churchyard.
—KGF Vissers